Characteristics of the mud shale reservoirs in coal-bearing strata and resources evaluation in the eastern margin of the Ordos Basin, China

Abstract

As the co-exploration and co-production of unconventional gas have become a new trend of the unconventional gas exploration and development in the eastern margin of the Ordos Basin, this study focuses on the distribution, pore characteristics, geochemical properties, and mineral composition of the mud shale in the coal-bearing strata. The results show that the mud shale in the coal-bearing strata is distributed relatively stably with an average cumulative thickness of 77.60 m and a buried depth of 200–2400 m, increasing from east to west. The total organic carbon content of mud shale is relatively high, ranging from 0.14% to 39.9%, and the thermal maturity ranges from 0.23% to 2.49%, affected by both buried depth and magmatic intrusion. The organic matter type of the mud shale is dominated by type III, favorable for gas generation. The mineral composition of mud shale is mainly clay minerals and quartz, with low brittle minerals content (averaging 30.34%) and high kaolinite content (averaging 59.23%). Pores and micro-fissures are relatively developed in the mud shale, dominated by intergranular pores, organic pores, and the micro-fissures developed between brittle mineral crystals, within crystals and between clay mineral particles, with a porosity of 1.05%–1.59% and a permeability of 0.001–0.142 (×10−3µm2). The specific surface area of pores in mud shale is 12.31–28.99 m2/g, and the total pore volume is 0.0146–0.0483 cm3/g. Mesopores and micropores (mainly slit shaped pores) provide the main pore volume of mud shale, and micropores contribute most of the specific surface area. The controlling factors on pore development include the total organic carbon, thermal maturity, and inorganic minerals composition. The total amount of shale gas resources is 2.49 × 1012 m3, and the Linxian-Xingxian area and Shilou-Daning area are the potential favorable zones for shale gas exploration and development.

The influence of physicochemical environment on the distribution and abundance of mangrove gastropods in Ngurah Rai Forest Park Bali, Indonesia

“…Generally, the higher smooth granules (clay), the higher Corganic content will be found in the mangroves area. This is consistent with study conducted by Serrano et al (2016) and Chen et al (2020) that clay has a good ability to storage C-organic because it has dense pores while sand has large pores so that organic matter is easily carried by currents. The C-organic content in the substrate is very important as a source of nutrients for gastropods in the mangrove ecosystems.…”

Mechanical Properties of Different Lithological Rocks: A Case Study of the Coal Measure Strata in the Eastern Margin of Ordos Basin, China

“…The coal measure strata in the study area are the Benxi Formation, Taiyuan Formation, and Shanxi Formation from bottom to top. The sedimentary system dominated by barrier coast lagoon system is developed in the Benxi Formation and Taiyuan Formation, while the coastal shallow sea lagoon tidal delta sedimentary system is developed in Shanxi Formation, which is a typical marine land transitional facies sedimentary environment [25][26][27][28]. The coal measure strata of these different sedimentary systems have different reservoir combinations of "coalbed methane-tight sandstone gas-shale gas."…”

Pore structure characteristics of shale in coal-bearing strata: In the case of the Shanxi formation of lower Permian in Huainan coalfield in China

“…Previous studies have shown that the pore structure of coal measure shale is affected by many factors. In China, studies on coal measure shales of Taiyuan Formation in Huainan coalfield, Shanxi Formation, and Taiyuan Formation in Qinshui Basin have found that organic matter can promote the development of nanoscale pores (Chen et al, 2020; Ge et al, 2020; Pan et al, 2017), significantly promoted the pore development of <50 nm, followed by the content of clay minerals, while quartz inhibited the pore development (Yan et al, 2017; Yuan et al, 2021). However, Zhang et al (2017) studied the pore structure of coal measure shales of Yan’an Formation and Taiyuan Formation in the northeastern margin of the Ordos Basin and found that organic matter and clay content had a poor correlation with total surface area and porosity, and believed that single factor had no significant influence on pore structure (Zhang et al, 2017).…”